The exception of lis pendens is an objection against the admissibility of the claim. The general power of the tribunal to hear the claim is not contested, but the special situation that a claim on the same cause of action is pending before another forum is alleged to preclude the tribunal from asserting jurisdiction. This essay focuses on the exception of lis pendens raised before the International Court of Justice or the United Nations Security Council when both organs are simultaneously engaged in the settlement of the same dispute.